It is known that metal oxide such as titanium oxide may be used as photocatalyst by absorbing light energy. Using such effect, there have been attempts to remove environmental pollution such as the sources of air pollution and water pollution. In the past, it was general to use metal oxide by fixing it in a carrier such as metal, ceramic and activated carbon. However, in the case of fixing a photocatalyst on a surface, the photocatalyst can detach from the carrier. Also, it is not easy to change photocatalyst according to the shape of a reactor because the photocatalyst is fixed. In the case of using photocatalyst in a fixed carrier, it is not easy to replace photocatalyst whose activity is lowered because of aging and repetitive uses.